U.S. patent application number 14/718453 was filed with the patent office on 2015-11-26 for spark plug for internal combustion engine.
The applicant listed for this patent is DENSO CORPORATION, NIPPON SOKEN, INC.. Invention is credited to Takanobu AOCHI, Kaori DOI, Noriaki NISHIO, Masamichi SHIBATA.
Application Number | 20150337791 14/718453 |
Document ID | / |
Family ID | 54555696 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150337791 |
Kind Code |
A1 |
AOCHI; Takanobu ; et
al. |
November 26, 2015 |
SPARK PLUG FOR INTERNAL COMBUSTION ENGINE
Abstract
A spark plug has a housing, a pair of center and ground
electrodes configured to define a spark gap therebetween, a guide
member and an oblique surface. The ground electrode has a standing
portion that stands distalward from a distal end of the housing.
The guide member is configured to guide the flow of an air-fuel
mixture in a combustion chamber of an engine to the spark gap. The
guide member protrudes distalward from the distal end of the
housing at a different circumferential position from the ground
electrode. The oblique surface is formed at the distal end of the
housing so as to be circumferentially positioned between the guide
member and the standing portion of the ground electrode. The
oblique surface is oblique to the axial direction of the spark plug
so that the radial distance between the oblique surface and the
center electrode decreases in the distalward direction.
Inventors: |
AOCHI; Takanobu;
(Nishio-shi, JP) ; DOI; Kaori; (Kariya-shi,
JP) ; SHIBATA; Masamichi; (Toyota-shi, JP) ;
NISHIO; Noriaki; (Ichinomiya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON SOKEN, INC.
DENSO CORPORATION |
Nishio-city
Kariya-city |
|
JP
JP |
|
|
Family ID: |
54555696 |
Appl. No.: |
14/718453 |
Filed: |
May 21, 2015 |
Current U.S.
Class: |
313/120 |
Current CPC
Class: |
H01T 1/20 20130101; F02P
15/001 20130101; H01T 13/02 20130101 |
International
Class: |
F02P 15/00 20060101
F02P015/00; H01T 13/02 20060101 H01T013/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2014 |
JP |
2014-106282 |
Claims
1. A spark plug for an internal combustion engine, the spark plug
comprising: a tubular housing; a tubular insulator retained in the
housing; a center electrode secured in the insulator with a distal
end portion of the center electrode protruding outside the
insulator; a ground electrode configured to define a spark gap
between the center and ground electrodes in an axial direction of
the spark plug, the ground electrode having a standing portion that
stands distalward from a distal end of the housing; a guide member
configured to guide the flow of an air-fuel mixture in a combustion
chamber of the internal combustion engine to the spark gap, the
guide member protruding distalward from the distal end of the
housing at a different circumferential position from the ground
electrode; and an oblique surface formed at the distal end of the
housing so as to be positioned in a circumferential direction of
the spark plug between the guide member and the standing portion of
the ground electrode, the oblique surface being oblique to the
axial direction of the spark plug so that the radial distance
between the oblique surface and the center electrode decreases in
the distalward direction.
2. The spark plug as set forth in claim 1, wherein the oblique
surface is formed to extend in the circumferential direction of the
spark plug only within an angular range of less than or equal to
90.degree. between the guide member and the standing portion of the
ground electrode.
3. The spark plug as set forth in claim 2, wherein the oblique
surface is formed to extend in the circumferential direction of the
spark plug over the entire axial range.
4. The spark plug as set forth in claim 1, wherein the oblique
surface is formed to extend in the circumferential direction of the
spark plug over an entire angular range of less than or equal to
90.degree. between the guide member and the standing portion of the
ground electrode.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on and claims priority from
Japanese Patent Application No. 2014-106282 filed on May 22, 2014,
the content of which is hereby incorporated by reference in its
entirety into this application.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to spark plugs for internal
combustion engines.
[0004] 2 Description of the Related Art
[0005] As ignition means in internal combustion engines, such as
engines of motor vehicles, there are used spark plugs which have a
spark gap formed between a center electrode and a ground electrode
that are axially opposed to each other. Those spark plugs discharge
a spark across the spark gap, thereby igniting an air-fuel mixture
in a combustion chamber.
[0006] In the combustion chamber, there is formed a flow of the
air-fuel mixture, such as a swirl flow or tumble flow. With the
flow of the air-fuel mixture moderately flowing also in the spark
gap, it is possible to ensure the ignition capability of the spark
ping (i.e., the capability of the spark plug to ignite the air-fuel
mixture).
[0007] However, depending on the mounting posture (or mounting
state) of the spark plug to the internal combustion engine, part of
the ground electrode, which is joined to a distal end of a housing
of the spark plug, may be located upstream of the spark gap with
respect to the flow of the air-fuel mixture. In this case, the flow
of the air-fuel mixture in the combustion chamber may be blocked by
the ground electrode, thereby being stagnated in the vicinity of
the spark gap. As a result, the ignition capability of the spark
plug may be lowered. That is, the ignition capability of the spark
plug may vary depending on the mounting posture of the spark plug
to the internal combustion engine. In particular, in lean-burn
internal combustion engines which have been widely used in recent
years, the combustion stability may be lowered depending on the
mounting posture of the spark plug.
[0008] However, it is generally difficult to control the mounting
posture of a spark plug to an internal combustion engine, i.e.,
difficult to control the circumferential position of the ground
electrode of the spark plug relative to the internal combustion
engine. This is because the mounting posture of the spark plug to
the internal combustion engine varies depending on the state of
formation of a male-threaded portion in the housing of the spark
plug and the degree of fastening the male-threaded portion into a
female-threaded bore formed in the engine.
[0009] To solve the above problem, Japanese Patent Application
Publication No. JPH09148045A discloses two techniques for
preventing the flow of the air-fuel mixture from being blocked by
the ground electrode. The first technique is to form a slot-like
hole in the ground electrode. The second technique is to fix the
ground electrode to the housing through a plurality of thin
plate-shaped members.
[0010] However, in the case of applying the first technique, the
strength of the ground electrode may be lowered due to the
formation of the slot-like hole in the ground electrode. Moreover,
if the ground electrode was formed to have a large thickness for
ensuring the strength thereof, it would become easier for the
ground electrode to impede the flow of the air-fuel mixture in the
combustion chamber.
[0011] On the other hand, in the case of applying the second
technique, the shape of the ground electrode is complicated, thus
increasing the manufacturing cost and lowering the
productivity.
SUMMARY
[0012] According to exemplary embodiments, there is provided a
spark plug for an internal combustion engine. The spark plug has a
tubular housing, a tubular insulator, a center electrode, a ground
electrode, a guide member and an oblique surface. The insulator is
retained in the housing. The center electrode is secured in the
insulator with a distal end portion of the center electrode
protruding outside the insulator. The ground electrode is
configured to define a spark gap between the center and ground
electrodes in an axial direction of the spark plug. The ground
electrode has a standing portion that stands distalward from a
distal end of the housing. The guide member is configured to guide
the flow of an air-fuel mixture in a combustion chamber of the
internal combustion engine to the spark gap. The guide member
protrudes distalward from the distal end of the housing at a
different circumferential position from the ground electrode. The
oblique surface is formed at the distal end of the housing so as to
be positioned in a circumferential direction of the spark plug
between the guide member and the standing portion of the ground
electrode. The oblique surface is oblique to the axial direction of
the spark plug so that the radial distance between the oblique
surface and the center electrode decreases in the distalward
direction.
[0013] The above spark plug has the following advantages.
[0014] First, with the guide member, it is possible to guide the
flow of the air-fuel mixture in the combustion chamber of the
engine to the spark gap regardless of the mounting posture of the
spark plug to the engine.
[0015] More specifically, even when the standing portion of the
ground electrode is located upstream of the spark gap with respect
to the flow of the air-fuel mixture in the combustion chamber, it
is still possible to guide the flow of the air-fuel mixture passing
by the standing portion of the ground electrode to the spark gap by
the guide member. Consequently, it is possible to suppress
stagnation of the flow of the air-fuel mixture in the vicinity of
the spark gap. As a result, it is possible to secure a stable
ignition capability of the spark plug.
[0016] Moreover, with the oblique surface, it is possible to
effectively stabilize the ignition capability of the spark
plug.
[0017] More specifically, the flow of the air-fuel mixture in the
combustion chamber is not always in a direction perpendicular to
the axial direction of the spark plug. Instead, the flow of the
air-fuel mixture may have a vector component toward the proximal
side in the axial direction of the spark plug. In this case,
without the oblique surface, a spark discharged across the spark
gap would be blown toward the housing by the flow of the air-fuel
mixture flowing into the spark gap. Consequently, the flame might
be cooled by the housing, thereby resulting in a misfire. In
particular, the flow of the air-fuel mixture passing through a
circumferential gap between the guide member and the standing
portion of the ground electrode is apt to be accelerated by the
guidance of the guide member. If the accelerated flow of the
air-fuel mixture has a vector component toward the proximal side,
it would be particularly easy for the spark to be blown by the flow
of the air-fuel mixture to the housing and thereby cause a misfire
to occur.
[0018] However, in the above-described spark plug, with the oblique
surface, it is possible to alter to the distal side the direction
of the flow of the air-fuel mixture passing through the
circumferential gap. Consequently, even when the flow of the
air-fuel mixture is inclined toward the proximal side at an angle
of, for example, about 60.degree. to the axial direction of the
spark plug, it is still possible to alter the flow into a flow in
the spark gap which has a considerably smaller vector component
toward the proximal side or has a vector component toward the
distal side. As a result, it is possible to reliably prevent a
misfire from occurring, thereby ensuring the ignition capability of
the spark plug.
[0019] To sum up, the above-described spark plug can secure, with a
simple configuration, a stable ignition capability regardless of
the mounting posture of the spark plug to the engine.
[0020] In a further implementation, the oblique surface may be
formed to extend in the circumferential direction of the spark plug
only within an angular range of less than or equal to 90.degree.
between the guide member and the standing portion of the ground
electrode. Moreover, in this case, it is preferable that the
oblique surface is formed to extend in the circumferential
direction of the spark plug over the entire axial range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention will be understood more fully from the
detailed description given hereinafter and from the accompanying
drawings of exemplary embodiments, which, however, should not be
taken to limit invention to the specific embodiments but are for
the purpose of explanation and understanding only.
[0022] In the accompanying drawings:
[0023] FIG. 1 is a perspective view of a distal part of a spark
plug according to a first embodiment;
[0024] FIG. 2 is a side view of the distal part of the spark
plug;
[0025] FIG. 3 is a cross-sectional view taken along the line
III-III in FIG. 2;
[0026] FIG. 4 is a cross-sectional view taken along the line IV-IV
in FIG. 3;
[0027] FIG. 5 is a cross-sectional view illustrating a modification
of the shape of an oblique surface formed in the spark plug
according to the first embodiment;
[0028] FIG. 6 is a schematic view illustrating advantages of the
spark plug according to the first embodiment;
[0029] FIG. 7 is a Gross-sectional view taken along the line
VII-VII in FIG. 6;
[0030] FIG. 8 is a schematic view illustrating the first step of a
method of manufacturing the spark plug according to the first
embodiment;
[0031] FIG. 9 is a schematic view illustrating the second step of
the method of manufacturing the spark plug;
[0032] FIG. 10 is a schematic view illustrating the third step of
the method of manufacturing the spark plug;
[0033] FIG. 11 is a schematic view illustrating the fourth step of
the method of manufacturing the spark plug; FIG. 12 is a schematic
view illustrating the fifth step of the method of manufacturing the
spark plug;
[0034] FIG. 13 is a schematic view illustrating the sixth step of
the method of manufacturing the spark plug;
[0035] FIG. 14 is a schematic view illustrating the seventh and
eighth steps of the method of manufacturing the spark plug;
[0036] FIG. 15 is a perspective view of a distal part of a spark
plug according to a comparative example;
[0037] FIG. 16 is a side view of the distal part of the spark plug
according to the comparative example, wherein a standing portion of
a ground electrode is located upstream of a spark gap with respect
to the flow of an air-fuel mixture in a combustion chamber;
[0038] FIG. 17 is a cross-sectional view taken along the line
XVII-XVII in FIG. 16; and
[0039] FIG. 18 is a perspective view of a distal part of a spark
plug according to a second embodiment.
DESCRIPTION OF EMBODIMENTS
[0040] Exemplary embodiments will be described hereinafter with
reference to FIGS. 1-18. It should be noted that for the sake of
clarity and understanding, identical components having identical
functions throughout the whole description have been marked, where
possible, with the same reference numerals in each of the figures
and that for the sake of avoiding redundancy, descriptions of the
identical components will not be repeated.
First Embodiment
[0041] This embodiment illustrates a spark plug 1 that is designed
to be used as ignition means in an internal combustion engine of
for example, a motor vehicle.
[0042] More specifically, the spark plug 1 is designed to ignite an
air-fuel mixture in a combustion chamber of the engine. The spark
plug 1 has one axial end to be connected to an ignition coil not
shown) and the other axial end to be placed inside the combustion
chamber. In addition, hereinafter, as shown in FIG. 1, the axial
side where the spark plug 1 is to be connected to the ignition coil
will be referred to as "proximal side"; and the other axial side
where the spark plug 1 is to be placed inside the combustion
chamber will be referred to as "distal side".
[0043] As shown in FIGS. 1-4, the spark plug 1 according to the
present embodiment includes: a tubular housing (or metal shell) 2;
a tubular insulator 3 retained in the housing 2; a center electrode
4 secured in the insulator 3 such that a distal end portion 41 of
the center electrode 4 protrudes outside the insulator 3; and a
ground electrode 5 configured to protrude distalward (i.e., toward
the distal side) from a distal end 21 of the housing 2 and define a
spark gap G between the center and ground electrodes 4 and 5 in the
axial direction of the spark plug 1.
[0044] Specifically, in the present embodiment, the ground
electrode 5 is substantially L-shaped to have a standing portion 51
and an opposing portion 52. The standing portion 51 is provided to
stand (or protrude) distalward from the distal end 21 of the
housing 2. The opposing portion 52 extends perpendicular to the
standing portion 51 and has an opposing surface 53 that opposes the
distal end portion 41 of the center electrode 4 in the axial
direction of the spark plug 1 through the spark gap G formed
therebetween.
[0045] Moreover, the spark plug 1 according to the present
embodiment further includes a guide member 22 for guiding the flow
of the air-fuel mixture hi the combustion chamber of the engine to
the spark gap G. The guide member 22 protrudes distalward from the
distal end 21 of the housing 2 at a different circumferential
position front the standing portion 51 of the ground electrode 5.
The guide member 22 has a flat guide surface 221 that faces the
ground electrode 5 in the circumferential direction of the spark
plug 1.
[0046] Furthermore, in the present embodiment, at the distal end 21
of the housing 2, there is fanned an oblique surface 23 which is
oblique to the axial direction of the spark plug I such that the
oblique surface 23 is directed radially inward as it extends
distalward. In other words, the oblique surface 23 is oblique to
the axial direction of the spark plug 1 so that the radial distance
between the oblique surface 23 and the center electrode 3 decreases
in the distalward direction. Moreover, the oblique surface 23 is
circumferentially positioned between the guide member 22 and the
standing portion 51 of the ground electrode 5.
[0047] In other words, the oblique surface 23 is positioned within
a circumferential gap (or a flow-passing gap through which the flow
of the air-fuel mixture passes) 11 formed between the guide member
22 and the standing portion 51 of the ground electrode 5. The
angular range of the circumferential gap 11 is less than or equal
to 90.degree.. That is, the expression "the oblique surface 23 is
circumferentially positioned between the guide member 22 and the
standing portion 51 of the ground electrode 5" used hereinafter
denotes that the oblique surface 23 is circumferentially positioned
within the angular range of less than or equal to 90.degree. (i.e.,
not the angular range of greater than or equal to 90.degree.)
between the guide member 22 and the standing portion 51 of the
ground electrode 5.
[0048] In the present embodiment, the oblique surface 23 is formed
only within the angular range of less than or equal to 90.degree.
(or within the flow-passing gap 11) between the guide member 22 and
the standing portion 51 of the ground electrode 5.
[0049] Moreover, in the present embodiment, the oblique surface 23
is formed over the entire angular range of less than or equal to
90.degree. between the guide member 22 and the standing portion 51
of the ground electrode 5.
[0050] Furthermore, in the present embodiment, as shown in FIG. 4,
the oblique surface 23 is formed over substantially the entire
radial thickness of the housing 2.
[0051] However, it should be appreciated that the oblique surface
23 may be formed over only part of the radial thickness of the
housing 2, as shown in FIG. 5.
[0052] The oblique surface 23 may be oblique at an angle in the
range of, for example, 30 to 70.degree. to the axial direction of
the spark plug 1. In other words, the oblique angle of the oblique
surface 23 to the axial direction of the spark plug 1 may be in the
range of for example, 30 to 70.degree..
[0053] In the present embodiment, the oblique surface 23 is formed
as a taper surface such that on a plane that includes a central
axis of the spark plug 1 (i.e., on the paper surface of FIG. 4),
the oblique surface 23 is in the shape of a straight line.
[0054] However, it should be appreciated that the oblique surface
23 may be formed as a curved surface such that on the plane that
includes the central axis of the spark plug 1, the oblique surface
23 is in the shape of a curved line.
[0055] In the present embodiment, the oblique surface 23 has its
distal end positioned proximalward from the distal end portion 41
of the center electrode 4. Moreover, the distal end of the oblique
surface 23 protrudes distalward from the distal end 21 of the
housing 2 by, for example, 0.7 mm or more
[0056] In the present embodiment, as shown in FIGS. 1-2, the ground
electrode 5 has a protrusion 54 provided on the opposing surface 53
of the opposing portion 52. The spark gap G is formed between the
distal end portion 41 of the center electrode 4 and the protrusion
54 of the ground electrode 5. In addition, the distal end portion
41 of the center electrode 4 and the protrusion 54 of the ground
electrode 5 are each constituted by a noble metal chip.
[0057] In the present embodiment, as shown in FIGS. 1-3, the guide
member 22 has the shape of a quadrangular prism and is arranged to
extend from the distal end 21 of the housing 2 distalward in the
axial direction of the spark plug 1. The guide member 22 has its
distal end positioned distalward from the spark gap G. Moreover,
the guide member 22 has its radial width greater than its
circumferential width. Further, the circumferential width of the
guide member 22 is less than the circumferential width of the
standing portion 51 of the ground electrode 5. In addition, that
one of the two circumferential side faces of the guide member 22
which circumferentially faces the standing portion 51 of the ground
electrode 5 constitutes the guide surface 221 of the guide member
22.
[0058] Next, a method of manufacturing the spark plug 1 according
to the present embodiment will be described. This method includes
first to eighth steps.
[0059] In the first step, as shown in FIG. 8, the housing 2 is
prepared which has both the insulator 3 and the center electrode 4
assembled therein.
[0060] In the second step, as shown in FIG. 9, a quadrangular
prism-shaped electrode material 50 for forming the ground electrode
S is welded, for example by resistance welding, to the distal end
21 of the housing 2.
[0061] In addition, in this step, though not shown in FIG. 9 and
subsequent FIGS. 10-14, the noble metal chip for forming the
protrusion 54 of the ground electrode 5 is welded to a
predetermined area on a side face of the electrode material 50.
[0062] In the third step, as shown in FIG. 10, the electrode
material 50 is bent to form the substantially L-shaped ground
electrode 5. Consequently, the spark gap G is formed between the
center electrode 4 and the ground electrode 5.
[0063] In the fourth step, as shown in FIG. 11, at a predetermined
position on the distal end 21 of the housing 2, a groove 211 is
formed so as to penetrate the housing 2 in a radial direction of
the spark plug 1. In addition, the position of formation of the
groove 211 is predetermined based on the positional relationship
between the center electrode 4, the ground electrode 5 and the
guide member 22 which will be fitted in the groove 211 in the next
step.
[0064] In the fifth step, as shown in FIG. 12, a proximal end
portion of the guide member 22 is fitted in the groove 211.
[0065] In the sixth step, as shown in FIG. 13, the proximal end
portion of the guide member 22 is welded, for example by resistance
welding, to peripheral portions of the groove 211 in the housing
2.
[0066] In the seventh step, a shown in FIG. 14, an oblique
surface-forming member 230 is arranged between the guide member 22
and the standing portion 51 of the ground electrode 5 on the distal
end 21 of the housing 2.
[0067] In addition, the oblique surface-forming member 230 may be
made of the same material as the housing 2, the ground electrode 5
and the guide member 22, such as a nickel alloy.
[0068] In the eighth step, referring again to FIG. 14, the oblique
surface-forming member 230 is welded, for example by resistance
welding, to the distal end 21 of the housing 2, thereby forming the
oblique surface 23. As a result, the spark plug 1 is finally
obtained.
[0069] In addition, in the eighth step, the oblique surface-forming
member 230 may also be simultaneously welded to the standing
portion Si of the ground electrode 5 and the guide member 22.
[0070] It should be noted that laser welding may be used instead of
resistance welding in the above second, sixth and eighth steps of
the method.
[0071] The above-described spark plug 1 according to the present
embodiment has the following advantages.
[0072] In the present embodiment, the spark plug 1 includes the
guide member 22. Consequently, it is possible to guide the flow F
of the air-fuel mixture in the combustion chamber of the engine to
the spark gap G regardless of the mounting posture of the spark
plug 1 to the engine.
[0073] Specifically, as shown in FIG. 7, even when the standing
portion 51 of the ground electrode 5 is located upstream of the
spark gap G with respect to the flow F of the air-fuel mixture in
the combustion chamber, it is still possible to guide the flow F of
the air-fuel mixture passing by the standing portion 51 of the
ground electrode 5 to the spark gap G by the guide member 22.
Consequently, it is possible to suppress stagnation of the flow F
of the air-fuel mixture in the vicinity of the spark gap G. As a
result, it is possible to secure a stable ignition capability of
the spark plug 1. is Moreover, in the present embodiment, the spark
plug 1 further has the oblique surface 23 formed at the distal end
21 of the housing 2 so as to be positioned in the circumferential
direction of the spark plug 1 between the guide member 22 and the
standing portion 51 of the ground electrode 5. The oblique surface
23 is oblique to the axial direction of the spark plug 1 such that
the oblique surface 23 is directed radially inward as it extends
distalward (i.e., the radial distance between the oblique surface
23 and the center electrode 3 decreases in the distalward
direction). Consequently, with the oblique surface 23, it is
possible to effectively stabilize the ignition capability of the
spark plug 1.
[0074] Specifically, the flow F of the air-fuel mixture flowing to
the distal part of the spark plug 1 is not always in a direction
perpendicular to the axial direction of the spark plug 1. Instead,
as shown in FIG. 6, the flow F of the air-fuel mixture flowing to
the distal part of the spark plug 1 may have a vector component
toward the proximal side in the axial direction of the spark plug
1. In this case, without the oblique surface 23, a spark S
discharged across the spark gap G would be blown toward the housing
2 by the flow F of the air-fuel mixture flowing into the spark gap
G (see FIG. 16). Consequently, the flame might be cooled by the
housing 2, thereby resulting in a misfire. In particular, the flow
F of the air-fuel mixture passing through the circumferential gap
11 between the guide member 22 and the standing portion 51 of the
ground electrode 5 is apt to be accelerated by the guidance of the
guide member 22. If the accelerated flow F of the air-fuel mixture
has a vector component toward the proximal side, it would be
particularly easy for the spark S to be blown by the flow F to the
housing 2 and thereby cause a misfire to occur.
[0075] However, in the present embodiment, as shown in FIG. 6, with
the oblique surface 23, it is possible to alter to the distal side
the direction of the flow F of the air-fuel mixture passing through
the circumferential gap 11. Consequently, even when the flow F of
the air-fuel mixture is inclined toward the proximal side at an
angle of, for example, about 60.degree. to the axial direction of
the spark plug 1, it is still possible to alter the flow F into a
flow F1 in the spark gap G; the flow F1 has a considerably smaller
vector component toward the proximal side than the flow F or has a
vector component toward the distal side. As a result, it is
possible to reliably prevent a misfire from occurring, thereby
ensuring the ignition capability of the spark plug 1.
[0076] Moreover, in the present embodiment, the oblique surface 23
is formed to extend in the circumferential direction of the spark
plug 1 only within the angular range of the circumferential gap 11
(i.e., the angular range of less than or equal to 90.degree.
between the guide member 22 and the standing portion 51 of the
ground electrode 5).
[0077] With the above formation of the oblique surface 23, it is
possible to sufficiently secure the ignition capability of the
spark plug 1.
[0078] Specifically, if the oblique surface 23 was formed outside
the angular range of the circumferential gap 11 and the spark S was
extended in length by the flow F of the air-fuel mixture flowing
into the spark gap G via the circumferential gap 11, the spark S
may reach the oblique surface 23 depending on the position of the
oblique surface 23. In contrast, with the above formation of the
oblique surface 23 according to the present embodiment, it is
possible to prevent the above problem from occurring, thereby
enhancing the ignition capability of the spark plug 1.
[0079] Furthermore, in the present embodiment, the oblique surface
23 is formed to extend in the circumferential direction of the
spark plug 1 over the entire angular range of the circumferential
gap 11.
[0080] With the above formation of the oblique surface 23, it is
possible for the oblique surface 23 to more reliably fulfill the
function of altering the direction of the flow F of the air-fuel
mixture. Consequently, it is possible to more effectively stabilize
the ignition capability of the spark plug 1.
[0081] To sum up, the spark plug 1 according to the present
embodiment can secure, with a simple configuration, a stable
ignition capability regardless of the mounting posture of the spark
plug 1 to the engine.
Comparative Example
[0082] FIG. 15 shows the overall configuration of a spark plug 9
according to a comparative example.
[0083] As shown in FIG. 15, the spark plug 9 differs from the spark
plug 1 according to the first embodiment only in that unlike the
spark plug 1, the spark plug 9 has no oblique surface 23 formed
therein.
[0084] As shown in FIG. 17, since the spark plug 9 also has the
guide member 22, the flow F of the air-fuel mixture in the
combustion chamber of the engine can be guided by the guide member
22 to the spark gap G formed in the spark plug 9 regardless of the
mounting posture of the spark plug 9 to the engine.
[0085] However, without the oblique surface 23 described in the
first embodiment, the ignition capability of the spark plug 9 may
be lowered when the flow F of the air-fuel mixture has a vector
component toward the proximal side in the axial direction of the
spark plug 9.
[0086] Specifically, referring to FLU 16, assume that the standing
portion 51 of the ground electrode 5 is located upstream of the
spark gap G with respect to the flow F of the air-fuel mixture in
the combustion chamber and the flow F of the air-fuel mixture has a
vector component toward the proximal side. More particularly,
assume that the flow F of the air-fuel mixture is inclined toward
the proximal aide at an angle of, for example, about 60.degree. to
the axial direction of the spark plug 9. In this ease, as shown in
FIG. 17, part of the flow F of the air-fuel mixture passing by the
standing portion Si of the ground electrode 5 is guided (or altered
in direction) by the guide surface 221 of the guide member 22 to
the spark gap G. Consequently, the part of the flow F of the
air-fuel mixture is accelerated when passing through the
circumferential gap 11 between the guide member 22 and the standing
portion 51 of the ground electrode 5. Moreover, as shown in FIG.
16, the flow F2 of the air-fuel mixture in the spark gap G is
inclined toward the proximal side. Consequently, a spark S
discharged across the spark gap G is blown toward the housing 2 by
the flow F2 of the air-fuel mixture. As a result, the flame may be
cooled by the housing 2, thereby resulting in a misfire.
[0087] Accordingly, without the oblique surface 23 described in the
first embodiment, the ignition capability of the spark plug 9 may
be lowered depending on the mounting posture of the spark plug 9 to
the engine and on the condition of the flow F of the air-fuel
mixture in the combustion chamber.
Second Embodiment
[0088] This embodiment illustrates a spark plug 1 which has almost
the sane configuration as the spark plug 1 according to the first
embodiment; accordingly, only the difference therebetween will be
described hereinafter.
[0089] In the first embodiment, as described previously, the
oblique surface 23 is formed to extend in the circumferential
direction of the spark plug 1 only within the angular range of the
circumferential gap 11 (see FIG. 1).
[0090] In comparison, in the present embodiment, as shown in FIG.
18, the oblique surface 23 is formed over the entire circumference
of the distal end 21 of the housing 2. That is, the oblique surface
23 is formed at the distal end 21 of the housing 2 so as to extend
in the circumferential direction of the spark plug 1 not only
within the angular range of the circumferential gap 11 but also
outside the angular range of the circumferential gap 11.
[0091] With the above configuration, it is possible to easily form
the oblique surface 23, thereby facilitating the manufacture of the
spark plug I.
[0092] While the above particular embodiments have been shown and
described, it will be understood by those skilled in the art that
various modifications, changes, and improvements may be made
without departing from the spirit of the present invention.
[0093] For example, in the above-described first embodiment, the
spark plug 1 has only the single guide member 22 formed on one
circumferential side of the standing portion 51 of the ground
electrode 5 and only the single oblique surface 23 formed between
the guide member 22 and the standing portion 51 of the ground
electrode 5.
[0094] However, the spark plug 1 may be modified to have a pair of
guide members 22 formed respectively on opposite circumferential
sides of the standing portion 51 of the ground electrode 5 and a
pair of oblique surfaces 23 each of which is formed between a
corresponding one of the guide members 22 and the standing portion
51 of the ground electrode 5.
* * * * *